Summary:Instead of relying on `push_back()` to guarantee exponential growth,
delegate to `expand_noinit`. This removes the duplication of logic
between the two functions, and significantly speeds up short appends.

```
$ _bin/folly/test/fbstring_benchmark_using_jemalloc --bm_min_usec=100000
                                                          Before:             After:
============================================================================ ===================
./folly/test/FBStringTestBenchmarks.cpp.h       relative  time/iter  iters/s  time/iter  iters/s
============================================================================ ===================
...
BM_push_back_fbstring(1)                                     7.51ns  133.20M     6.87ns  145.49M
BM_push_back_fbstring(23)                                  175.08ns    5.71M   173.92ns    5.75M
BM_push_back_fbstring(127)                                 586.02ns    1.71M   585.70ns    1.71M
BM_push_back_fbstring(1024)                                  3.30us  302.81K     3.41us  293.13K
BM_short_append_fbstring(23)                               367.01ns    2.72M   179.45ns    5.57M
BM_short_append_fbstring(1024)                               9.33us  107.20K     5.72us  174.95K
...
============================================================================ ===================
```

Reviewed By: philippv

Differential Revision: D3075249

fb-gh-sync-id: 497775ba3fc707bf50821a3cf10fb9d247b9352d
shipit-source-id: 497775ba3fc707bf50821a3cf10fb9d247b9352d

Summary: It is perfectly reasonable to need to feature macros when checking configuration, and the configuration is needed to know if features.h exists, so put it in the same file.

Reviewed By: yfeldblum

Differential Revision: D3072255

fb-gh-sync-id: 0f253dd1fa2f4a95adb11f11c45e6b86ef9c25bc
shipit-source-id: 0f253dd1fa2f4a95adb11f11c45e6b86ef9c25bc

Summary: This is needed to avoid a circular dependency.

Reviewed By: yfeldblum

Differential Revision: D3072037

fb-gh-sync-id: 546a46fd68f25f0c5b027d4d938335b2711d8fdd
shipit-source-id: 546a46fd68f25f0c5b027d4d938335b2711d8fdd

Reviewed By: pritamdamania

Differential Revision: D3068807

fb-gh-sync-id: 0b45ab678e2ec5565eb379540576527cf8b1d308
shipit-source-id: 0b45ab678e2ec5565eb379540576527cf8b1d308

Summary:Upgrade UncaughtExceptionCounter to use std::uncaught_exceptions on Visual Studio 2015 Update 1
Closes https://github.com/facebook/folly/pull/358

Reviewed By: yfeldblum

Differential Revision: D3066005

Pulled By: Orvid

fb-gh-sync-id: 6bc7129aa794257b1f6e7a084139d8a3a52fa4a8
shipit-source-id: 6bc7129aa794257b1f6e7a084139d8a3a52fa4a8

Summary: Something that Windows very definitely lacks. This is a fun one.

Reviewed By: yfeldblum

Differential Revision: D2979661

fb-gh-sync-id: e23c1db0cb8655b22308b874bd421a7cc1e4759e
shipit-source-id: e23c1db0cb8655b22308b874bd421a7cc1e4759e

Summary:[Folly] Remove `pthread_yield` support.

* It is not actually part of POSIX - rather, `sched_yield` is.
* In C++, we should be using `std::this_thread::yield` anyway.

Reviewed By: Gownta

Differential Revision: D3056221

fb-gh-sync-id: 2fea55dd7b715149327987d61e5a573ad0455330
shipit-source-id: 2fea55dd7b715149327987d61e5a573ad0455330

Summary:We currently set the session context to the
default of common name, this allows session
context to be set to a different value
for different applications

Reviewed By: ngoyal

Differential Revision: D3059769

fb-gh-sync-id: 185afeb487c2c62dcf44f96076bd05871692c7ab
shipit-source-id: 185afeb487c2c62dcf44f96076bd05871692c7ab

Summary:ASAN needs to know about the stack extents. Currently it has no knowledge of
fibers and so it can give false positives, particularly in cases of no-return
(think exceptions).

See: https://github.com/google/sanitizers/issues/189

This change along with a related ASAN diff fixes that, and I've verified it
fixes false positive test failures I'm seeing when throws happen from fibers.

Also rips out some hacks that attempted to work around the limitations of
ASAN these changes should fix.

This change depends on:
D3017630
D2952854
D3017619

And will also depend on rollout of libasan.so to /usr/local/fbcode platform dirs on all machines.

Reviewed By: andriigrynenko

Differential Revision: D2952899

fb-gh-sync-id: 19da779227c6c0f30c5755806325aa4cba364cfe
shipit-source-id: 19da779227c6c0f30c5755806325aa4cba364cfe

Summary: Because including the root portability header just to get a couple of defines to be able to enable things is a waste. In addition, it would be nice if the config defines are never needed outside of the portability headers.

Reviewed By: yfeldblum

Differential Revision: D3059651

fb-gh-sync-id: 1cb9910d850ea015616a598808556b4815b3fb74
shipit-source-id: 1cb9910d850ea015616a598808556b4815b3fb74

Summary: Fix folly/test:thread_local_test in the shared library scenario by moving onThreadExit into libfolly_thread_local.so, avoiding the crash when a user's .so is dlclosed.

Reviewed By: andriigrynenko

Differential Revision: D2919287

fb-gh-sync-id: ecc4220fd40203289366eb1a6391b8b6d971e65f
shipit-source-id: ecc4220fd40203289366eb1a6391b8b6d971e65f

Summary: Older compilers do not have have `std::make_unique`. We have `folly::make_unique` which does the same job, and because we already have `using namespace folly` in this file it suffices to erase the `using std::make_unique` line.

Reviewed By: eduardosuarez

Differential Revision: D3058089

fb-gh-sync-id: a5a5eb54e2bc0ba7ef0880f2b5680a79d1f41d37
shipit-source-id: a5a5eb54e2bc0ba7ef0880f2b5680a79d1f41d37

Summary: [Folly] Remove an outdated/inapplicable comment from `folly/Portability.h`.

Reviewed By: Gownta

Differential Revision: D3055909

fb-gh-sync-id: c17fdcc7de13fe5a9bb38bb4498a006ec71a61e2
shipit-source-id: c17fdcc7de13fe5a9bb38bb4498a006ec71a61e2

Summary: We don't have it on Windows :(

Reviewed By: yfeldblum

Differential Revision: D2978397

fb-gh-sync-id: 388bc450ce269559825ebfb78e3646533c2e1153
shipit-source-id: 388bc450ce269559825ebfb78e3646533c2e1153

Summary:easy:
`options.parentDeathSignal_` is `int`, and second argument of `prctl` is `unsigned long`. Adding explicit cast.

hard:
this change is fixing a real problem when building folly with Clang 3.9.0. The [[ https://github.com/llvm-mirror/clang/commit/f4ddf94ecbd9899a497151621f3871545e24e93b | new alignment implementation ]] in `-O3` generates code that breaks folly's `ParentDeathSubprocessTest.ParentDeathSignal`.
For the following snipped of code:
```lang=cpp
  if (options.parentDeathSignal_ != 0) {
    if (prctl(PR_SET_PDEATHSIG, options.parentDeathSignal_, 0, 0, 0) == -1) {
      return errno;
    }
  }
```
LLVM generates the following assembly:
```lang=asm
   0x000000000040a77b <+347>:   mov    0x28(%r14),%rsi
   0x000000000040a77f <+351>:   test   %esi,%esi
   0x000000000040a781 <+353>:   je     0x40a7a1 <folly::Subprocess::prepareChild(folly::Subprocess::Options const&, __sigset_t const*, char const*) const+385>
   0x000000000040a783 <+355>:   mov    $0x1,%edi
   0x000000000040a788 <+360>:   xor    %edx,%edx
   0x000000000040a78a <+362>:   xor    %ecx,%ecx
   0x000000000040a78c <+364>:   xor    %r8d,%r8d
   0x000000000040a78f <+367>:   xor    %eax,%eax
   0x000000000040a791 <+369>:   callq  0x405ad0 <prctl@plt>
```
`%rsi` is a 64-bit register, on the line 1 value of `0x28(%r14)` is loaded to this register. That address points to `options.parentDeathSignal_`, which is a 32-bit value, set to 10 somewhere in a test. After that load:
```
rsi            0x7f000000000a
```
Notice it is not 10 (0xa), there is some garbage value in the upper part of the register. On the line 2, the lower part of this register is checked if it is zero, which corresponds to the first if statement. Then lines 4-8 prepare for `prctl` call. The value of the second argument is passed via `%rsi`, but the upper 32 bits were not cleared. This makes the function call generate `Invalid argument` error.
With the added explicit cast, notice a call `movslq %eax,%rsi`, which moves a signed 32-bit value of `%eax` (which contains `options.parentDeathSignal_`) to unsigned 64-bin `%rsi`:
```
   0x000000000040a77b <+347>:   mov    0x28(%r14),%rax
   0x000000000040a77f <+351>:   test   %eax,%eax
   0x000000000040a781 <+353>:   je     0x40a7a4 <folly::Subprocess::prepareChild(folly::Subprocess::Options const&, __sigset_t const*, char const*) const+388>
   0x000000000040a783 <+355>:   movslq %eax,%rsi
   0x000000000040a786 <+358>:   mov    $0x1,%edi
   0x000000000040a78b <+363>:   xor    %edx,%edx
   0x000000000040a78d <+365>:   xor    %ecx,%ecx
   0x000000000040a78f <+367>:   xor    %r8d,%r8d
   0x000000000040a792 <+370>:   xor    %eax,%eax
   0x000000000040a794 <+372>:   callq  0x405ad0 <prctl@plt>
```

Reviewed By: yfeldblum

Differential Revision: D3051611

fb-gh-sync-id: fc0f809bc4be0eed79dc5a701717efa27fedc022
shipit-source-id: fc0f809bc4be0eed79dc5a701717efa27fedc022

Summary:Add a new method to MPMCQueue:
```
template <class Clock, typename... Args>
  bool tryWriteUntil(const std::chrono::time_point<Clock>& when,
                     Args&&... args) noexcept
```
This allows you to write producers which terminate reliably in the absence of consumers.

Returns `true` if `args` was enqueued, `false` otherwise.

`Clock` must be one of the types supported by the underlying call to `folly::detail::Futex::futexWaitUntil`; at time of writing these are `std::chrono::steady_clock` and `std::chrono::system_clock`.

Reviewed By: nbronson

Differential Revision: D2895574

fb-gh-sync-id: bdfabcd043191c149f1271e30ffc28476cc8a36e
shipit-source-id: bdfabcd043191c149f1271e30ffc28476cc8a36e

Summary:Allow HTTPSession to have a movable read
callback independent of the openssl check.

This allows other downstream transports to
deliver app data more efficiently.

Reviewed By: w-o-o, knekritz

Differential Revision: D3023517

fb-gh-sync-id: ff27c0e14f7364ad7d7b0028ef740b2678dbcb4c
shipit-source-id: ff27c0e14f7364ad7d7b0028ef740b2678dbcb4c

Summary:defined(FOLLY_TLS) is guarded once in the test, so we should
guard for it throughout.  Also a missing header for some platforms.

Reviewed By: yfeldblum

Differential Revision: D3049797

fb-gh-sync-id: 5d66c71dda94c57a2e50aee96d55be1c574bf921
shipit-source-id: 5d66c71dda94c57a2e50aee96d55be1c574bf921

Summary:This commit fixes compiler errors when Constexpr.h was included
on gcc before cstring (or string.h) was included. Also, qualify
the call to strlen with the std namespace.

Reviewed By: yfeldblum

Differential Revision: D3047417

fb-gh-sync-id: 7a50dac2e9449b149062896f34fa5e864f767943
shipit-source-id: 7a50dac2e9449b149062896f34fa5e864f767943

Summary: Also, add error checking back in, and remove the empty WIN32 implementation.

Reviewed By: francis-ma

Differential Revision: D3047494

fb-gh-sync-id: 5a2a18cd1ca675a081ad2a9252c765ab56527b6b
shipit-source-id: 5a2a18cd1ca675a081ad2a9252c765ab56527b6b

Summary:Adding support for resetting a specified function's timer.

"Resetting a function's timer" effectively means "canceling whatever next runs it would have had, and treating it as though it were just added".
When `resetFunctionTimer` is called, the specified function's interval (timer) will be reset, and it will execute after its initially-specified `startDelay`. If the `startDelay` is zero, the function will execute immediately, and then be scheduled as before - once every `interval` milliseconds.

Motivation: batch processing of updates, where both a size and time limit are in play. If the size limit is reached, it makes sense to reset the timer for the scheduled function.

Differential Revision: D3045868

fb-gh-sync-id: a5ceb0069c04a77fdab16b61679987ee55484e89
shipit-source-id: a5ceb0069c04a77fdab16b61679987ee55484e89

Summary:The `init()` function uses the previous value of `lock_`, but that is
uninitialized and the compiler can issue a warning about it. It is
also potentially undefined behavior because it is not guaranteed that
the address of `lock_` is taken before `init()` (in which case the it
would be just an indeterminate value).

Since it is not very useful to initialize only one slot and leave the
others uninitialized, we can just have a single `init()` that
zero-initializes all the slots.

Reviewed By: dcolascione

Differential Revision: D3042629

fb-gh-sync-id: de1633b02eb1c891e310f2d5d2cfc5376cd41d5f
shipit-source-id: de1633b02eb1c891e310f2d5d2cfc5376cd41d5f

Reviewed By: ot

Differential Revision: D3045850

fb-gh-sync-id: ee19b146c43410d8d8804c9bfe79c3811394b10e
shipit-source-id: ee19b146c43410d8d8804c9bfe79c3811394b10e

Summary:On systems that do not have gflags or glog installed globally,
but only locally as static libraries, our configure check failed for
glog because we were checking it prior to gflags.

glog depends on gflags, but when the libraries are static, there is
no explicit dependency information available and the linker fails.

This resolves the issue by checking for gflags first; this causes
configure to add an implicit `-lgflags` for the subsequent glog
tests.

Reviewed By: yfeldblum

Differential Revision: D3044138

fb-gh-sync-id: 5e07ce52842c6e4cff796560672bf950e2fafe6c
shipit-source-id: 5e07ce52842c6e4cff796560672bf950e2fafe6c

Summary: This was wrong and is like better solved, not with a shim layer, but by not using such a platform-specific function in the first place.

Reviewed By: yfeldblum

Differential Revision: D3001253

fb-gh-sync-id: 460cc46b1c9adc3d229a07cb290270f7afbbb1e0
shipit-source-id: 460cc46b1c9adc3d229a07cb290270f7afbbb1e0

Summary:PicoSpinLock only works on x86_64, Arm64, and ppc64 (i.e.,
not 32-bit).  Add a bit of gating so we can continue to run tests and
use headers when compiling for i386.

Reviewed By: yfeldblum

Differential Revision: D2991328

fb-gh-sync-id: b0d0c229508f65dff62b24fdd9d80c799cd97935
shipit-source-id: b0d0c229508f65dff62b24fdd9d80c799cd97935

Summary: Address the exception safety hole described in https://fburl.com/scopeguard-oops. Addnditional noexcept to the places that need it.

Reviewed By: dcolascione

Differential Revision: D3033015

fb-gh-sync-id: 8dfec103bbc86abef425585371994756d3df0a14
shipit-source-id: 8dfec103bbc86abef425585371994756d3df0a14

Summary:The vast majority of `folly::dynamic` array initializations are
single-line and with no nested arrays, so we can fix them with a
syntactic codemod. This also fixes a couple of singletons.

For empty arrays:
```
codemod '((?:folly::)?)(dynamic\s+\w+\s*=\s*)({\s*})' '\1\2\1dynamic::array'
```

For non-empty ones:
```
codemod '((?:folly::)?)(dynamic\s+\w+\s*=\s*)(?:{\s*([^{}]+?)\s*})' '\1\2\1dynamic::array(\3)'
```

Reviewed By: igorsugak

Differential Revision: D3030338

fb-gh-sync-id: 3e56704a6c6294d6f6270e42a1776d991a7938df
shipit-source-id: 3e56704a6c6294d6f6270e42a1776d991a7938df

Summary: This allows HTTPTransactions to be held back until the transport is replay-safe.

Reviewed By: siyengar

Differential Revision: D2974083

fb-gh-sync-id: 037b14c24a80c828a25e483b6873a8e782af0cb4
shipit-source-id: 037b14c24a80c828a25e483b6873a8e782af0cb4

Summary: Windows has it, but it doesn't define lstat, and a few other functions have other names.

Reviewed By: yfeldblum

Differential Revision: D3003096

fb-gh-sync-id: e7bc210390d18806c8c89cbc18711bb7a728e12f
shipit-source-id: e7bc210390d18806c8c89cbc18711bb7a728e12f

Summary: This was causing a bunch of SIGBUS's on ARM platforms.

Reviewed By: yfeldblum, mzlee

Differential Revision: D3013458

fb-gh-sync-id: 6d3f60c3f59d16cd3454e3a4231b967e5378724a
shipit-source-id: 6d3f60c3f59d16cd3454e3a4231b967e5378724a

Summary:SSLContext and AsyncSSLSocket are growing with a lot of code that is
OpenSSL-specific, and it may be good to refactor some of these before it gets
out of hand.

This is also useful to reduce complexity as we some additional features such as ServerHello parsing and TLS Cached Info (D2936570)

Main changes:
 * Created a subdirectory folly/io/async/ssl to refactor code from folly/io/async. We may want to consider moving this out of folly/io/async
 * Moved OpenSSLPtrTypes.h to folly/io/async/ssl/OpenSSLPtrTypes.h
 * Moved 'OpenSSLUtils' from SSLContext to separate file OpenSSLUtils.{h,cpp}
 * Moved TLSExtensions and ClientHelloInfo from AsyncSSLSocket to TLSDefinitions.h

Reviewed By: siyengar

Differential Revision: D2978707

fb-gh-sync-id: a21f02947aeffccc447da2124a91cc99315df1c7
shipit-source-id: a21f02947aeffccc447da2124a91cc99315df1c7

Summary:This diff uses the x86 "pause" instruction or its equivalent when
spinning in the MicroLock slow loop.  This gives a hint to the processor
that it should devote more resources to the other execution contexts
sharing the same core.  This diff also removes an mfence on x86 by using
a slightly stronger memory model on the preceding compare_exchange_weak,
and switches to a more portable way of invoking sched_yield().

Reviewed By: dcolascione

Differential Revision: D3018568

fb-gh-sync-id: 02e0ab3a9d9bb9901eddf54e45b71cbb7758a227
shipit-source-id: 02e0ab3a9d9bb9901eddf54e45b71cbb7758a227

Summary:After DR95 the single braces dispatch to the copy constructor
(http://www.open-std.org/jtc1/sc22/wg21/docs/cwg_defects.html#1467),
so it is not possible anymore to initialize a singleton dynamic array
using the braces syntax. The initializer list constructor already had
a special case for empty lists, which unconditionally called the
default constructor if defined.

This diff deprecates the braces syntax and defines the following alternative:
```
dynamic empty = dynamic::array;
dynamic a = dynamic::array(1, 2, "foo");
```

Reviewed By: luciang, yfeldblum

Differential Revision: D3013423

fb-gh-sync-id: a0cf09dfd96e9806044f7c3bf3592c637a9bc932
shipit-source-id: a0cf09dfd96e9806044f7c3bf3592c637a9bc932

Summary:Guarding this the same way it is done in
detail/CacheLocality.cpp

Reviewed By: yfeldblum

Differential Revision: D3013288

fb-gh-sync-id: a1cc65cccc5cdf32339a739853c27a11ecd98ba0
shipit-source-id: a1cc65cccc5cdf32339a739853c27a11ecd98ba0

Summary: Because Windows' defines seem to get in the way more than they help.

Reviewed By: yfeldblum

Differential Revision: D2989507

fb-gh-sync-id: 148f390ef6adf977bffa2262aa76839b2bf4f507
shipit-source-id: 148f390ef6adf977bffa2262aa76839b2bf4f507

Summary: [Folly] A warning for the `portability` headers.

Reviewed By: mzlee, Orvid, meyering

Differential Revision: D3014442

fb-gh-sync-id: f6557d8021dc2a50a656685492d717fdbff1124a
shipit-source-id: f6557d8021dc2a50a656685492d717fdbff1124a

Summary: tmpdir does not work on all platforms. TemporaryDirectory is more robust.

Reviewed By: yfeldblum

Differential Revision: D3013866

fb-gh-sync-id: 51e2b7ec2348eb95b99c125a27bb2aca2b87ac21
shipit-source-id: 51e2b7ec2348eb95b99c125a27bb2aca2b87ac21

Summary: Windows has it, but it doesn't define pid_t. It also doesn't define ssize_t, and it's not worth a separate header for a single typedef, so define it here as well.

Reviewed By: yfeldblum

Differential Revision: D3001168

fb-gh-sync-id: 3722270181c200bbcf39043960f81609c854b132
shipit-source-id: 3722270181c200bbcf39043960f81609c854b132

Summary: clang would complain about losing integer precision. Use unsigned for offset calculation.

Reviewed By: luciang

Differential Revision: D3011253

fb-gh-sync-id: 10cb603708a22bf0e57f41b2486ffca4f5bf7a14
shipit-source-id: 10cb603708a22bf0e57f41b2486ffca4f5bf7a14